The present invention relates generally to surgical tourniquets. More particularly, the present invention relates to various aspects of a system and method for controlling pressure in a surgical tourniquet utilizing feedback from a flow detection sensor incorporated in the tourniquet control system.
Surgical tourniquets are widely used during surgical procedures to occlude the flow of blood in a portion of a limb during the procedure, particularly in connection with arthroscopic procedures relating to the hand, wrist, elbow, foot, and knee, in which the existence of a bloodless field in the appropriate portion of a patient""s limb may be required. Surgical tourniquets are similarly useful in other procedures in which the creation of a bloodless field is desirable, including nerve grafting and harvesting. It is important that pressure be maintained by a surgical tourniquet despite the manipulation by a surgeon of the limb in which blood flow is being occluded, where the manipulation tends to affect the pressure within the tourniquet and the pressure distribution of the tourniquet on the extremity. Also, it is important that the tourniquet pressure be minimized to reduce the potential of adverse effects due to the constriction of the tourniquet. It is also important that the surgical tourniquet be easy to use and physically stable so that the surgeon may focus his attention on other aspects of the surgery.
Typical non-invasive blood pressure measurements are generally made by either of two methods. In the first method, a stethoscope is placed beneath or below a pressure cuff. The pressure cuff is then inflated to a pressure in excess of the patient""s systolic blood pressure, causing occlusion of the blood flow past the pressure cuff. The pressure in the cuff is then gradually decreased, while a person taking the pressure measurement listens through the stethoscope. As the blood pressure overcomes the pressure in the cuff, blood begins flowing past the cuff. This blood flow causes sounds called Korotkoff sounds to be generated. These sounds are distinctive of the blood flow past the pressure cuff, and abate once the blood pressure fully reopens the arteries constricted by the pressure cuff. By identifying the Korotkoff sounds, and monitoring the decreasing pressure in the cuff, the pressure at which blood pressure exceeds cuff pressure can be identified. Determinations can be made of both systolic and diastolic blood pressures by monitoring Korotkoff sounds associated with a higher pressure (systolic) and a lower pressure (diastolic). This method is sometimes referred to as the auscultatory method.
A second method of non-invasive blood pressure measurement, called oscillometric measurement, is also accomplished using a pressure cuff and decreasing pressure. In oscillometric pressure measurement, however, a column of mercury is generally used to measure the pressure in the cuff. As the patient""s blood pressure exceeds the cuff pressure, blood flow past the cuff causes the pressure in the cuff to pulse in time with the blood flow past the cuff. The mercury column being used to measure pressure thus also pulses, allowing a person taking the blood pressure measurement to visually identify blood flow past the pressure cuff. The patient""s blood pressure can thus be determined by monitoring the mercury column for the start of pulsing, and the pressure at which the pulsing begins.
The pressure necessary to occlude blood flow in a tourniquet is dependant on the blood pressure of the patient on whom the tourniquet is applied. When the pressure of the tourniquet exceeds the blood pressure, the heart of the patient is unable to pump blood past the tourniquet location. Typically, the tourniquet pressure cuff is inflated in excess of the blood pressure to ensure occlusion of blood flow past the tourniquet. When a surgical tourniquet is applied to the arm, over-pressurization of the surgical tourniquet of 50-75 mm Hg is common. When a surgical tourniquet is applied to a leg, over-pressurization of the surgical tourniquet of 75-100 mm Hg is common.
Over-pressurization of a tourniquet can cause injury to a patient on whom the tourniquet is being used. Neural and vascular injuries can occur due to the pressure in use causing physical trauma. Accordingly, the pressure used to occlude blood flow past the tourniquet should be kept to the minimum necessary to overcome the systolic pressure, thus preventing the pumping of blood past the tourniquet. Contrarily, high pressures ensure occlusion of blood flow.
In addition to the constraints of simply using a surgical tourniquet to occlude blood flow, the use of the surgical tourniquet to provide a barrier to allow intravenous regional anesthesia (IVRA) raises additional concerns, particularly with the dangers associated with the flow of the anesthesia past the barrier and into the body of the patient. Furthermore, the need to flush the anesthesia from the limb at the conclusion of an operation requires the allowance of systolic flow to both test veins and arteries potentially affected by the surgery, and to displace the anesthesia used. The allowance of systolic flow while preventing diastolic flow requires accurate determination of the onset of flow past a surgical tourniquet or tourniquets being used to form the barrier.
The present invention is directed towards a system and method for controlling the pressure within a surgical tourniquet so as to occlude blood flow past a tourniquet. The surgical tourniquet uses a fluid medium to vary the pressure within the tourniquet. The fluid medium may be air. The addition or removal of air from the surgical tourniquet is controlled such as through a controller described in our patent applications, Ser. Nos. 09/280,312 and 09/504,131, herein incorporated in their entirety by reference thereto.
The flow of blood past a tourniquet creates a signal which is transmitted to the tourniquet by the physical contact between the patient and the tourniquet. The signal comprises pressure variations in the veins and arteries of an extremity to which the surgical tourniquet is applied. These pressure variations may be a signal audible to a listener, or a variation of the cuff pressure caused by the pulsing associated with normal blood flow. These pressure variations may be transmitted from the surgical tourniquet to the controller via the fluid medium used to inflate the tourniquet. By incorporating a sensor to detect these signals, a feedback loop can be incorporated into the controller allowing the controller to detect blood flow past the tourniquet when the tourniquet is inflated. When blood flow past the pressure cuff of the surgical tourniquet is detected, the controller can increase pressure into the surgical tourniquet, thereby providing a means for ensuring that the flow of blood past the surgical tourniquet is occluded.
In a first embodiment, the present invention is a surgical tourniquet controller which includes an occlusion sensor, and a means for increasing pressure in a surgical tourniquet when the occlusion sensor detects blood flow past the surgical tourniquet. The occlusion sensor may detect oscillometric indications or Korotkoff sounds as a means for detecting flow past the surgical tourniquet.
In an alternate embodiment, the present invention comprises a method for controlling a surgical tourniquet. The method includes the steps of inflating a pressure cuff to an initial pressure, detecting blood flow past a pressure cuff when blood flows past the pressure cuff, incrementally increasing pressure in the pressure cuff in response to detected flow past the pressure cuff, determining whether the increased pressure in the surgical tourniquet has occluded blood flow past the tourniquet, and when blood flow has not been occluded, continuing to incrementally increase blood cuff pressure until blood flow past the tourniquet is occluded, or may additionally incrementally increase the cuff pressure until a threshold pressure is achieved.
In a still further embodiment, the present invention comprises a computer readable medium for providing instructions to a surgical tourniquet controller, the medium tangibly embodying instructions which, when executed by a computer, cause a surgical tourniquet controller to inflate a pressure cuff to an initial pressure, detect blood flow past a pressure cuff when blood flows past the pressure cuff, incrementally increase pressure in the pressure cuff when flow is detected past the pressure cuff, determine whether the increased pressure in the pressure cuff has occluded blood flow past the pressure cuff, and when blood flow has not been occluded, continuing to incrementally increase blood pressure until blood flow past the pressure cuff is occluded.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiment, and from the claims.